Added books in slovak language
Added czech book for security
Update URL to czech books

Change URL to official source
Added author for czech books
Merge pull request #1112 from grogy/slovak-books

Added books in slovak language
Merge pull request #1113 from grogy/czech-books

Added czech book for security
Merge branch 'czech-books-update' of github.com:grogy/free-programming-books into grogy-czech-books-update

Conflicts:
	free-programming-books-cs.md
Merge branch 'grogy-czech-books-update'
Merge pull request #8 from vhf/master

sync with vhf:master